238 DEVONIAN FOSSILS. 



half of the shell ; those near the margin of old specimens about 

 one line wide, gradually diminishing towards the beak. 

 Length 1 inch 2 lines, proportional width from beak to 

 opposite ventral margin -^-^q, length of anterior lunette ■^-^■^j 

 width of posterior end about y^^^^, depth of one valve about -^-^q. 



This species in size, shape, subtruncate anterior end, and coarse 

 concentric wrinkles of the anterior half becoming obsolete on 

 the posterior portion, almost exactly resembles the L. truncatus 

 (M^Coy) of the Upper Ludlow rock, but may be distinguished 

 easily by the strong divisional sulcus from the beak. I suspect 

 the fossil from Baggy Point, referred by Phillips (Pal. Eoss.) to 

 the Silurian so-called Cypricardia impressa of Sowerby, may be 

 found to belong rather to the present species. 



One young specimen, 5 lines long, of the left valve, and two 

 large specimens in opposition of the right valve, have occurred in 

 the sandstone of Marwood, N. Devon. 



{Col. University of Cambridge.) 



Clymenia quadrifera (M'Coy). 

 Sp. Char. Discoid, compressed, nearly two-thirds of the whorls 

 concealed ; whorls about four and a half, crossed by very mi- 

 nute sigmoid striae; periphery* narrow, obtusely rounded; septa 

 with the middle portion crossing the periphery small; first sinus 

 small, oblique, very obtusely rounded ; first lobe nearly in the 

 middle of the side, nearly square, slightly rhomboidal, length and 

 width about equal, truncated at the broad extremity, the angle 

 next the umbilicus rather more obtuse, and the other slightly 

 more acute than a right angle, sides subparallel ; second sinus 

 slightly higher than the first, extending with scarcely any cur- 

 vature to the umbilicus, its width double that of the lateral 

 lobe, which is placed nearly in the middle of the side ; dia- 



* In descriptions of discoid Cephalopod shells, as Ammonites, &c., con- 

 chologists almost invariably use the terms " hack or dorsal, and ventral,"' 

 exactly in the opposite sense to what anatomy or the position of the animal 

 would indicate. I therefore propose to use the term ''periphery " for that 

 part commonly called by describers of these shells the " back," or by ana- 

 tomists the " ventral aspect," as the use, at this late period, of the latter 

 term would bring much unnecessary confusion into the descriptions ; for 

 the opposite edge of the mouth I use the term " inner edge." In descri- 

 bing the septa of the same shells and for the same reason, instead of " dor- 

 sal lobe " I use the term " mid-lobe," or " inner mid-lobe,'' for the so-called 

 " ventral lobe " of Von Buch and all other describers. Instead of " first 

 lateral superior, first lateral inferior, and first, second, &c. auxiliary lobes," 

 terms which are unnecessarily complex, I propose to number and describe 

 the lobes simply as first lobe, second lobe, third lobe, &c., reckoning from 

 the outer mid-lobe, or, as it has usually been called, the dosral lobe. The 

 word sinus, I think, may be used instead of saddle for the inflexion between 

 each pair of lobes. 



